A Venturi mask is used to deliver a precise FiO2 to a COPD patient who is hypoxaemic but hypercapnic. The Venturi mask delivers accurate FiO2 because it operates on the principle of:
- A Variable performance based on the patient's inspiratory flow
- B Total oxygen reservoir that delivers 100% oxygen at any flow
- C Fixed performance by entraining a fixed ratio of room air to oxygen via the Bernoulli/Venturi effect ✓
- D Partial rebreather principle that recycles exhaled oxygen
Correct answer: C. Fixed performance by entraining a fixed ratio of room air to oxygen via the Bernoulli/Venturi effect
Explanation
The Venturi mask is a fixed-performance (high-flow) oxygen delivery device. Oxygen passes through a narrow jet, producing a pressure drop (Bernoulli principle) that entrains room air at a fixed ratio determined by the size of the entrainment port. This results in a total gas flow exceeding the patient's peak inspiratory flow rate, ensuring a stable and precise FiO2 (24%, 28%, 31%, 35%, or 40%) regardless of the patient's breathing pattern. This property makes it ideal for COPD patients where accidental delivery of high FiO2 risks abolishing hypoxic drive.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.